Wiring for fridge and battery charging 13 pin plug

The previous owner of my 2007 Series 6 Pageant rewired the two cables into a 13 pin plug. At a recent service the comment was made that only the fridge was connected and not the battery charging when the car was connected and ignition on. I see from UK trailer parts web site they recommend that pin 10 should only be used for either the fridge or the battery charge as to connect both could overload the car connection to that pin. Strange my dealer was not aware of this and if true a retrograde step from the old 7S plug where two separate pins were used. Any advice please before I start prodding about.